The life of a light emitting diode (LED), defined as time that elapses until the luminous flux maintenance factor lowers to 70%, exceeds 40000 hours (normal hours). Light emitting devices using LEDs as light emitting elements have been recently developed. For example, these devices can include a light source of an illumination apparatus such as a self-ballasted LED lamp, downlight or spotlight, the LED lamp being interchangeable with an incandescent bulb; a backlight of a thin shape television, liquid crystal display, mobile phone or various types of information terminals; and an indoor/outdoor signboard advertisement. Since the light emitting device has a long life, low consumption power, impact resistance, high responsiveness and high purity display color, it has been applied not only to general illumination apparatuses but also to industrial illumination apparatuses.
Light emitting devices using LEDs may be required to emit a large amount of light and have high efficiency, and may be further required to have high heat radiation performance so that they may be made compact. Additionally, a light emitting device is required to have heat resistance when it is being used for guide lights or emergency lights. In order to provide these characteristics, a substrate made of metal such as aluminum or a substrate made of ceramics such as alumina is used as a substrate on which LEDs are mounted. Such substrates excellent in thermal conductivity.
Typically a connector is used with aluminum and ceramic substrates as an electrically connecting unit of a substrate, and solder is used to form an electric connection of the connector to the substrate and an electric connection of the connector to a power supply wire. The ceramic substrate radiates a slight amount of outgas, and thus the junction temperature can be raised. However, solder is typically required to be set to 90° C. or lower in temperature to ensure reliability of the solder. Therefore, the junction temperature cannot be raised and sufficient heat resistance cannot be obtained.
Thus, a solderless electrically connecting unit is required to allow for raising the junction temperature. On the other hand, in a solderless electric connection, shadows of a connector and a wire fall on a light emitting face, light is absorbed, light emission efficiency is lowered, and light distribution is disrupted.
It is an object of the present invention to provide a light emitting device capable of improving heat resistance and light emission efficiency, and an illumination apparatus using the light emitting device.